1. Field of the Invention
This invention pertains to techniques for defining the shape, condition and function of blood vessels imbedded in human tissue.
2. Description of the Prior Art
Present commercial techniques utilize dye contrast radiography to produce arteriograms or venograms. Dye-contrast radiography requires that a radioopaque fluid be admitted into the bloodstream through the sidewall of the vessel, creating hazards to the health of the patient.
Continuous wave ultrasonic flow detectors using doppler techniques to detect the sound waves scattered from moving blood have been developed which avoid the necessity of introducing a fluid into the vessel and have given useful information when directed by hand and used to trace the circulation of animals and man. Continuous wave ultrasonic flow detectors in present use are generally limited to locating the blood vessels and determining the existence or non-existence of blood flow at various locations along the vessel. In part their use has been limited because it is generally believed that they encompass too great a region of tissue, i.e. lack adequate resolution, and are too difficult to direct for producing a picture equal in definition to that of dye-contrast radiographic arteriograms or venograms.
Pulsed ultrasonic doppler blood flow sensing is known. Known systems of this type, however, require extremely costly and sophisticated equipment and are very susceptible to signal noise when used to detect vessels deeply embedded in human tissue. Furthermore, the image produced shows the vessel along a plane perpendicular to the plane of the skin. This presents an immediate probelm of interpretation, since diagnosticians are more familiar with images parallel to the skin surface such as obtained from present state-of-the-art radiography.